Polyurethane urea elastic yarn having excellent uniformity and thermosetting property

ABSTRACT

The present invention provides a polyurethane urea elastic yarn and, more particularly, to a polyurethane urea elastic yarn having excellent uniformity and thermosetting property that is prepared by (1) preparing a prepolymer using a mixture containing 2 to 25 mol. % of 2,4′-diphenylmethane diisocyanate with respect to the total weight of the diisocyanate; (2) adding a chain extender to the prepolymer; and (3) preparing a polyurethane urea polymer having a solid content of at least 40 mol. % in the final polymer, stirring the polyurethane urea polymer to obtain a polyurethane urea spinning solution, and then aging and spinning the polyurethane urea spinning solution. The polyurethane urea elastic yarn prepared by the above method displays excellent uniformity and thermosetting properties, and union/knitted yarn using this elastic yarn displays no deterioration in uniformity, thus securing good fabric quality, and also enables thermosetting at low temperature, thus preventing thermal embrittlement of the relative yarn, and resulting in excellent yellowing and touch of the union/knitted yarn.

TECHNICAL FIELD

The present invention relates to a polyurethane urea elastic yarn having excellent uniformity and thermosetting property and, more particularly, to a polyurethane urea elastic yarn having excellent uniformity and thermosetting property that uses 2 to 25 mol. % of 2,4′-diphenylmethane diisocyanate in combination with at least one diisocyanate including 4,4′-diphenylmethane diisocyanate in the preparation of a polyurethane prepolymer and include at least 40 wt. % of the solid content in the final polyurethane urea polymer.

BACKGROUND ART

In general, polyurethane urea elastic yarn is obtained by reacting a polyol and an excess of a diisocyanate compound to form a first polymerization reactant that is a prepolymer having isocyanate groups at both ends of the polyol, dissolving the prepolymer in an appropriate solvent, adding a diamine- or diol-based chain extender to the resultant solution, adding a chain terminator such as mono-alcohol, mono-amine, etc. to produce a spinning solution for polyurethane urea yarn, and then performing dry and wet spinning procedures to obtain a polyurethane urea elastic yarn.

With the inherent properties such as excellent elasticity and elastic recovery property, the polyurethane urea elastic yarn is widely available in various uses. As the use of the polyurethane urea elastic yarn extends in its range, there is a consistent demand for additional properties to the existing polyurethane urea fibers.

DISCLOSURE OF INVENTION Technical Problem

Generally, when the polyurethane urea elastic yarn is woven in combination with relative yarns that are sensitive to heat (e.g., nylon, silk, cotton, etc.), the relative yarns are susceptible to thermal embrittlement under a high-temperature heat treatment for thermosetting during the post-process conducted after the blend knitting process, causing the fabric material to exhibit yellowing and deterioration of touch. As a solution to this problem, there is an increasing demand for a polyurethane urea elastic yarn capable of thermosetting even at low temperature, and sustained attempts have been made by many manufacturers of elastic yarns to enhance the thermosetting property of the polyurethane urea elastic yarn.

As for the methods of improving the thermosetting property of the polyurethane urea elastic yarn, for example, U.S. Pat. No. 5,948,875 discloses using at least 50 mol. % of 2-methyl-LS-pentane diamine as a chain extender; U.S. Pat. No. 6,472,494 describes using 23 to 55 mol % of 2,4′-diphenyl methane diisocyanate; and Korean Patent No. 0,942,359 filed by the present company discloses using 2 to 25 mol. % of 2,4′-diphenyl methane diisocyanate and adding 1,2-diaminopropane as an auxiliary chain extender. But, the techniques disclosed by these patents may cause deterioration in the thermal resistance and insufficient modulus and elastic recovery, reducing the tension of the yarn and increasing the float of the yarn during the spinning process to display poor spinning workability and poor uniformity of the yarn, which contributes to poor fabric quality in the case of union/knitted fabrics.

In other words, it is the current situation that there exists no established technique of manufacturing a polyurethane urea elastic yarn having excellent uniformity and thermosetting property at the same time.

Technical Solution

To solve the problems with the prior art, in accordance with a preferred embodiment of the present invention, there is provided a polyurethane urea elastic yarn having excellent uniformity and thermosetting property that is comprised of a polyol and diisocyanate polymer, the elastic yarn being produced by

(1) preparing a prepolymer using a mixture containing 2 to 25 mol. % of 2,4′-diphenyl methane diisocyanate with respect to the total weight of diisocyanate;

(2) adding a chain extender to the prepolymer to yield a polyurethane urea polymer; and

(3) preparing a polyurethane urea spinning solution having a solid content of at least 40 wt. % in the final polyurethane urea polymer and spinning the solution.

In accordance with another preferred embodiment of the present invention, the polyurethane urea elastic yarn may contain 75 to 98 mol. % of a first diisocyanate and 2 to 25 mol. % of a second diisocyanate, where the second diisocyanate is 2,4′-diphenyl methane diisocyanate. With its steric conformation relative to 4,4′-diphenyl methane diisocyanate, 2,4′-diphenyl methane diisocyanate has such a steric hindrance that weakens the intermolecular hydrogen bonding force and the intramolecular hydrogen bonding force of the hard segment. This has the same effect to increase the soft segment content and thus enhance the thermosetting property of the yarn.

In accordance with still another preferred embodiment of the present invention, the final polyurethane urea polymer may have a solid content of at least 40 wt. %. When the solid content is 40 wt. % or greater, the difference between the drying rate of the yarn surface and the solvent diffusion rate of the inside/surface of the yarn during the spinning process can be reduced to make the cross section of the yarn nearly circular, consequently with the cross section ratio close to 1.0. The uniformity of the yarn improves as the yarn has the cross section ratio nearer to 1.0.

The polyurethane urea elastic yarn of the present invention may have a cross section ratio of 1.20 or less, an Uster % of less than 1.0 and a heat set efficiency (HSE) of 50% or greater after a dry heat treatment at 170° C.

EFFECTS OF THE INVENTION

The present invention enables production of a polyurethane urea elastic yarn having excellent uniformity and thermosetting property that displays no deterioration in uniformity, securing good fabric quality, and enables thermosetting at low temperature to prevent thermal embrittlement of the relative yarn, resulting in excellent yellowing and touch of the union/knitted yarn.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a detailed description will be given as to the polyurethane urea elastic yarn of the present invention. The embodiment of the present invention can be modified in various forms and the range of the present invention is not limited to the embodiments hereinafter described. Throughout this specification, unless the context requires otherwise, the word “comprise”, “includes” or variations will be understood to imply to inclusion of any other component in addition to the stated one.

An elastic yarn according to an embodiment of the present invention may be prepared by polymerizing a polyol and an excess of diisocyanate to obtain a prepolymer, dissolving the prepolymer in an organic solvent, and then adding a chain extender and a chain terminator to the resultant solution to perform a second polymerization and prepare a spinning solution. In this regard, the chain extender and the chain terminator are added at once in a single step or separately in at least two steps.

Specific examples of the diisocyanate as used in the preparation of the polyurethane urea elastic yarn of the present invention may include 4,4′-diphenyl methane diisocyanate, 1,5′-naphthalene diisocyanate, 1,4′ -phenylene diisocyanate, hexamethylene diisocyanate, 1,4′-cyclohexane diisocyanate, 4,4′-dicyclohexyl methane diisocyanate, isophorone diisocyanate, etc. Among these diisocyanates, 2,4′-diphenyl methane diisocyanate can be used in combination with at least one diisocyanate including 4,4′-diphenyl methane diisocyanate. In this case, the content of 2,4′-diphenyl methane diisocyanate is in the range of 2 to 25 mol. %.

2,4′-diphenyl methane diisocyanate, which has a steric conformation relative to 4,4′-diphenyl methane diisocyanate, provides such a steric hindrance that weakens the intermolecular hydrogen bonding force and the intramolecular hydrogen bonding force of the hard segment. This has the same effect to increase the soft segment content and thus enhance the thermosetting property of the yarn.

When the content of 2,4′-diphenyl methane diisocyanate is less than 2 mol. %, it is too insignificant to make the effect to enhance the thermosetting property. When the content of 2,4′-diphenyl methane diisocyanate is greater than 25 mol. %, the modulus of the yarn abruptly decreases. It is therefore preferable that the content of 2,4′-diphenyl methane diisocyanate is within the defined range.

Specific examples of the polyol as used in the present invention may include polytetramethylene ether glycol, polytrimethylene ether glycol, polypropylene glycol, polycarbonate diol, a copolymer of a mixture of alkylene oxide and lactone monomer and poly(tetramethylene ether)glycol, a copolymer of 3-methyl-tetrahydrofuran and tetrahydrofurn, etc., which are used alone or as a mixture of at least two. But, the polyol may not be specifically limited to these examples.

The isocyanate of the prepolymer in the present invention preferably has a weight percentage of 1.7 to 4.1% for the sake of realizing properties suitable to the polymerurethane urea elastic yarn. The weight percentage of the isocyanate in the prepolymer less than 1.7% or greater than 4.1% may result in serous deterioration in the properties of the elastic yarn.

The chain extender is diamines. Specific examples of the diamines may include ethylene diamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminopbutane, 2,3-diaminobutane, 1,5-diaminopentane, 1,6-hexamethylenediamine, 1,4-cyclohexane diamine, etc., which may be used alone or as a mixture of at least two.

The chain exterminator of the polyurethane urea is an amine having one functional group.

Specific examples of the amine may include diethyl amine, mono-ethanol amine, dimethyl amine, etc.

The present invention is characterized by the fact that the final polyurethane urea polymer has a solid content of at least 40 wt. %. When the solid content is 40 wt. % or greater, the difference between the surface diffusion rate of the solvent in the yarn and the drying rate of the solvent on the surface of the yarn during the spinning process decreases due to lower solvent content relative to the solid content, thereby a more uniform drying is achieved, making the cross section of the polyurethane urea elastic yarn nearly circular, which means that the cross section ratio approaches 1.0. As the cross section ratio is closer to 1.0, the elastic yarn has a circular cross section with more uniform to improve the Uster %. Knitting a union/knitted fabric or performing a dyeing process using such an elastic yarn can enhance the fabric quality.

In addition, the present invention may add an appropriate combination of a steric hindrance phenol compound, a benzofuran-one compound, a semi-carbizide compound, a benzo triazole compound, a polymeric tertiary amine stabilizer, etc. to the spinning solution, in order to prevent discoloration or property deterioration of the polyurethane urea possibly caused by UV radiations, smog, and the heat treatment pertaining to the spandex process.

Furthermore, the polyurethane urea elastic yarn of the present invention may further include an additive, such as titanium dioxide, magnesium stearate, etc., in addition to the above-mentioned components.

Hereinafter, the present invention will be described in further detail with reference to the specific examples, which are given to exemplify the present invention and not construed to limit the scope of the present invention.

The measurement methods for NCO % of the polymer and the properties of the polyurethane urea elastic yarn are given as follows.

NCO % Measurement Method

NCO %=[100×2×NCO chemical formula weight×(capping ratio−1)]/ [(molecular weight of diisocyanate×capping ratio)+molecular weight of polyol]

In the above equation, the capping ratio is defined as the molar ratio of diisocyanate to polyol.

Strength and Elongation of Yarn

An automatic strength/elongation testing device (MEL series, Textechno Inc.) is used to measure strength and elongation properties of the yarn with a 10cm long sample at a tensile speed of 100 cm/min. The strength at break and the elongation are measured, and the load on the yarn at 200% elongation (i.e., 200% modulus) is also determined.

Cross Section Ratio of Yarn

The yarn is cut vertically in the lengthwise direction. With the cross section, the width W and the length H are measured using a microscope to determine the width-to-length ratio. The cross section is considered to be more circular with more uniformity as the width-to-length ratio is closer to 1.0.

Cross Section Ratio=W/H

In the equation, W is the length of the longest straight line crossing the cross section of the yarn;

-   -   and H is the length of the shortest straight line perpendicular         to the longest straight line crossing the cross section of the         yarn.

U % of Yarn

A Uster % testing device (KET-QT) is used to measure the Uster % by varying the speed of the feeding roller depending on the de of the yarn (30 m/min for 20 d). The thickness of a yarn unwound at a constant speed for 20 seconds is automatically checked by a sensor and averaged to draw a 0% reference line. When the thickness of the yarn checked by the sensor every unit time is greater than the reference value, a point is put in the positive (+) region above the 0% reference line. When the thickness of the yarn checked by the sensor every unit time is less than the reference value, a point is put in the negative (−) region below the 0% reference line. The degree of each point deviating from the 0% reference line is calculated in terms of area, which is expressed as U %. The lower U % indicates the yarn with more excellent uniformity.

U %=(the area deviating from the 0% reference line)/(the area below the 0% reference line)×100

Thermosetting Property of Yarn

Exposed to the atmosphere, an initial yarn (L0) is elongated by 100% (L1), subjected to a dry heat treatment at 170° C. for one minute, cooled down to the room temperature, and then measured in regards to the length (L2). The yarn, which gets loose under dry heat treatment, is subjected to a wet heat treatment at 100° C. for 30 minutes, dried at the room temperature, and then measured in regards to the length (L3). In this regard, L0, L1, L2, and L3 indicate the length of the yarn after each process (treatment).

The length of the yarn measured by performing a wet heat treatment at 100° C. for 30 minutes while the yarn is loose after dry heat treatment and then drying at the room temperature.

Dry thermosetting property (%)={(L2−L0)/(L1−L0)}×100

HSE (%)={(L3−L0)/(L1−L0)}×100

EXAMPLE 1

95 mol. % of 4,4′-diphenyl methane diisocyanate and 5 mol. % of 2,4′-diphenyl methane diisocyanate are mixed together at a capping ratio (CR) of 1.80. To the mixture are added a chain extender, which contains 80 mol. % of ethylene diamine and 20 mol. % of 1,2-diaminopropane, and a chain extender, which is diethyl amine. The ratio of the chain extender to the chain terminator is 10:1. The amine is used in such an amount as to have the total amine concentration of 7 mol. %. Dimethylacetamide is used as a solvent to prepare a polyurethane urea spinning solution in which the solid content of the final polymer is 45 wt. %.

The spinning solution thus obtained is subjected to dry spinning at 900 m/min to form a 20-denier 1-filament polyurethane urea elastic yarn. The elastic yarn is evaluated in regards to the properties, and the evaluation results are presented in Table 1.

EXAMPLE 2

The procedures are performed in the same manner as described in Example 1 to prepare a polyurethane urea elastic yarn, excepting that 85 mol. % of 4,4′-diphenyl methane diisocyanate and 15 mol. % of 2,4′-diphenyl methane diisocyanate are mixed together. The elastic yarn is evaluated in regards to the properties, and the evaluation results are presented in Table 1.

EXAMPLE 3

The procedures are performed in the same manner as described in Example 1 to prepare a polyurethane urea elastic yarn, excepting that 75 mol. % of 4,4′-diphenyl methane diisocyanate and 25 mol. % of 2,4′-diphenyl methane diisocyanate are mixed together. The elastic yarn is evaluated in regards to the properties, and the evaluation results are presented in Table 1.

EXAMPLE 4

The procedures are performed in the same manner as described in Example 1 to prepare a polyurethane urea elastic yarn, excepting that 70 mol. % of 4,4′-diphenyl methane diisocyanate and 30 mol. % of 2,4′-diphenyl methane diisocyanate are mixed together. The elastic yarn is evaluated in regards to the properties, and the evaluation results are presented in Table 1.

COMPARATIVE EXAMPLE 1

The procedures are performed in the same manner as described in Example 3 to prepare a polyurethane urea elastic yarn, excepting that the solid content of the final polymer is 35 wt. %. The elastic yarn is evaluated in regards to the properties, and the evaluation results are presented in Table 1.

COMPARATIVE EXAMPLE 2

The procedures are performed in the same manner as described in Example 1 to prepare a polyurethane urea elastic yarn, excepting that 100 mol. % of 4,4′-diphenyl methane diisocyanate is used. The elastic yarn is evaluated in regards to the properties, and the evaluation results are presented in Table 1.

TABLE 1 Example Comparative Example 1 2 3 4 1 2 First MDI/second MDI 95/5 85/15 75/25 70/30 75/25 100/0 NCO % 3.0 3.0 3.0 3.0 3.0 3.0 Solid content (%) of 45 45 45 45 35 45 final polymer Strength (g/d) 1.18 1.12 1.07 1.02 1.09 1.22 Elongation (%) 494 501 517 523 505 468 200% modulus (g) 4.0 3.8 3.4 2.7 3.7 4.1 Cross section ratio 1.20 1.12 1.08 1.06 1.31 1.64 U % 0.89 0.72 0.65 0.62 1.13 1.37 Dry heat set (%) 68.6 77.6 83.8 85.8 78.2 46.2 HSE (%) 48.4 57.4 64.2 66.6 58.2 23.8

As can be seen from Table 1, using at least 25 mol. % of 2,4′-diphenyl methane diisocyanate leads to excellent uniformity and thermosetting property but deterioration in the 200% modulus. Further, when the final polymer contains 2 to 25 mol. % of 2,4′-diphenyl methane diisocyanate and has a solid content of less than 40 wt. %, the elastic yarn is excellent in the thermosetting property but poor in the cross section ratio and U %.

Although a few exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described exemplary embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents. 

What is claimed is:
 1. A polyurethane urea elastic yarn having a cross section ratio of 1.20 or less and a HSE value of 50% or greater according to the following measurement methods: (1) Cross section ratio measurement method: measured by cutting the polyurethane urea elastic yarn vertically to a lengthwise direction, measuring width W and length H of the cross section and calculating the ratio, wherein as the cross section ratio approaches 1.0, the cross section of the elastic yarn is closer to a circle with higher uniformity, wherein the cross section ratio=W/H, wherein W is the length of the longest straight line crossing the cross section of the yarn; and H is the length of the shortest straight line intersecting perpendicular to the longest straight line W crossing the cross section of the yarn,

(2) HSE measurement method: measured by elongating an initial yarn L0 exposed to atmosphere by 100% (L1), performing a dry heat treatment on the yarn at 170° C. for one minute, cooling down the yarn to the room temperature, measuring the length of the yarn (L2), performing a wet heat treatment on dry heat treated yarn at 100° C. for 30 minutes while the yarn is loose, drying the yarn at room temperature, and then measuring the length of the yarn (L3), wherein HSE (%)={(L3−L0)/(L1−L0)}×100.
 2. The polyurethane urea elastic yarn as claimed in claim 1, wherein in the manufacture of the polyurethane urea elastic yarn, 2,4′-diphenyl methane diisocyanate is used at an amount of 2 to 25 mol. % with respect to the total weight of diisocyanate.
 3. The polyurethane urea elastic yarn as claimed in claim 1, wherein in the manufacture of the polyurethane urea elastic yarn, solid content of the polymer right before passing through a spinning nozzle is at least 40 wt. %.
 4. The polyurethane urea elastic yarn as claimed in claim 1, wherein in the manufacture of the polyurethane urea elastic yarn, NCO % during a first polymerization of polyol and diisocyanate is in the range of 1.7 to 4.1%. 